Solid polymer electrolyte fuel cell assmebly with gas passages in serial communication , and method of supplying reaction gas in fuel cell

ABSTRACT

A cell assembly ( 10 ) includes a first unit cell ( 14 ) and a second unit cell ( 16 ) which are stacked to each other. The first unit cell ( 14 ) has a first unified body ( 18 ), and the second unit cell ( 16 ) has a second unified body ( 20 ). A plurality of oxidizing gas passages ( 46, 58 ) and a plurality of fuel gas passages ( 56, 52 ) are provided in the cell assembly ( 10 ). The oxidizing gas passages ( 46 )in the first unit cell ( 14 ) and the oxidizing gas passages ( 58 ) in the second unit cell ( 16 ) are communicated in series to each other. The fuel gas passages ( 56 ) in the first unit cell ( 14 ) and the fuel gas passages ( 52 ) in the second unit cell ( 16 ) are communicated in series to each other.

TECHNICAL FIELD

[0001] The present invention relates to a solid polymer electrolyte fuelcell assembly including a plurality of unit cells integrally stacked toeach other, wherein each of the unit cells has a unified body includingan anode, a cathode and a solid polymer electrolyte membrane between theanode and the cathode. Further, the present invention relates to a fuelcell stack including a stack of the solid polymer electrolyte fuel cellassemblies, and a method of supplying a reaction gas to a fuel cell.

BACKGROUND ART

[0002] In general, a solid polymer electrolyte fuel cell (PEFC) includesa unit cell (unit power generation cell) configured by oppositelydisposing an anode and a cathode, each of which is mainly made fromcarbon, on both sides of an electrolyte membrane of a polymer ionexchange membrane (cation exchange membrane), to form a unified body(membrane-electrode assembly), and holding the unified body betweenseparators (bipolar plates). The solid polymer electrolyte fuel cell isgenerally used as a fuel cell stack having a specific number of the unitcells.

[0003] In the fuel cell of this type, when a fuel gas, for example, agas mainly containing hydrogen (hereinafter, referred to as “hydrogencontaining gas”) is supplied to the anode, hydrogen in the hydrogencontaining gas is ionized on the catalyst electrode and is migrated tothe cathode side via the electrolyte; and electrons generated by suchelectrochemical reaction are taken to an external circuit, to be used aselectric energy in the form of a direct current. In this case, since anoxidizing gas, for example, a gas mainly containing oxygen or air(hereinafter, referred to as “oxygen containing gas”) is supplied to thecathode, hydrogen ions, electrons and oxygen react with each other toproduce water on the cathode.

[0004] When a fuel cell stack is used as an on-vehicle power source, arelatively large output is required for the fuel cell stack. To meetsuch a requirement, a cell structure for making a size of a reactionplate (power generation plane) of a unit cell larger, and a cellstructure for stacking a large number of unit cells to each other havebeen adopted.

[0005] The former cell structure, however, has a problem that theenlarged size of each unit cell leads to the enlargement of the wholesize of the fuel cell stack and such a large-sized fuel cell stack isunsuitable as an on-vehicle power source. Accordingly, to obtain arelatively large output, the latter structure for stacking a largenumber of relatively compact unit cells to each other has been generallyadopted. However, as the number of the stacked unit cells becomeslarger, the temperature distribution tends to be generated in thestacking direction and also the drainage characteristic of waterproduced by the electrochemical reaction is degraded, thereby failing toensure a desired power generation performance.

[0006] To solve the above-described problems, the present invention hasbeen made, and an object of the present invention is to provide a solidpolymer electrolyte fuel cell assembly capable of effectively improvingthe power generation performance of each unit cell and reducing the sizeof the cell assembly with a simple structure, and a fuel cell stackcomposed of a stack of the cell assemblies.

[0007] Another object of the present invention is to provide a method ofsupplying a reaction gas in a fuel cell, which allows effective powergeneration of each unit cell and also allows improvement of the drainagecharacteristic of produced water.

DISCLOSURE OF INVENTION

[0008] According to the present invention, there is provided a solidpolymer electrolyte fuel cell assembly composed of a plurality of unitcells integrally stacked to each other, each of the unit cells having aunified body formed by holding a solid polymer electrolyte membranebetween an anode and a cathode, characterized in that reaction gaspassages for allowing at least one of reaction gases composed of a fuelgas and an oxidizing gas to flow in the plurality of unit cells areprovided in the cell assembly in such a manner that at least portions ofthe reaction gas passages are communicated in series to each other overthe unit cells. Here, the wording “at least portions” means at least twoor more of the plurality of the reaction gas passages, and also means atleast parts of the reaction gas passages.

[0009] With this configuration, in the cell assembly, a reaction gas inan amount required for cell reaction in the unit cell on the upstreamside and the unit cell on the downstream side is supplied to the unitcell on the upstream side, so that the flow rate of the reaction gassupplied in the cell assembly is increased, with a result that it ispossible to equalize humidities in the unit cells, and also to equalizecurrent density distributions in a plurality of the unit cells and henceto reduce a concentration over potential. Further, water produced in theunit cells can be effectively discharged only by increasing the flowvelocity of the reaction gas supplied to the cell assembly, and therebythe drainage characteristic of the whole cell assembly can be improved.

[0010] Since the reaction gas passages extend longer to connect aplurality of the unit cells to each other, a pressure drop is increased,so that it is possible to effectively improve the distributioncharacteristic of the reaction gas between respective unit cells and thedrainage characteristic of produced water. Further, since the cellassembly is a one-body composed of a plurality of unit cells, the fuelcell stack can be assembled by stacking the cell assemblies to eachother. As a result, it is possible to effectively simplify theworkability of assembly of the fuel cell stack as compared with theassembly of the fuel cell stack by stacking unit cells to each other.

[0011] In the cell assembly, at least two of the unit cells may havestructures different from each other. With this configuration, thestructure most suitable for cell reaction can be adopted for each unitcell. In this case, those, provided in the at least two of the unitcells, of the reaction gas passages for allowing at least one of a fuelgas and an oxidizing gas to flow therethrough, have cross-sectionsdifferent from each other. With this configuration, even if the amountof the reaction gas is reduced due to the electrochemical reaction, thereactions on the reaction planes in the unit cells can be equalized.

[0012] Concretely, the cross-sections of the reaction gas passagesprovided in the at least two of the unit cells may be made differentfrom each other by making the reaction gas passages different from eachother in terms of at least one of a passage depth, a passage width, andthe number of passages. With this configuration, if the passage depth ismade small, each unit cell can be thinned, so that the whole cellassembly can be miniaturized. If the passage width is made smaller orthe number of passages is reduced, the contact area between respectiveunit cells can be increased and thereby the, contact resistance can bereduced.

[0013] The cross-section of the reaction gas passage provided in each ofthose, on the downstream side in the flow direction of the reaction gas,of the at least two of the unit cells may be smaller than thecross-section of the reaction gas passage provided in each of those, onthe upstream side in the flow direction of the reaction gas, of the atleast two of the unit cells. Although the amount of produced water isincreased on the downstream side in the flow direction of the reactiongas, since the flow velocity of the reaction gas on the downstream sideis increased by reducing the passage cross-section, it is possible toeffectively improve the drainage characteristic of the produced water onthe downstream side.

[0014] The length of the reaction gas passage provided in each of those,on the downstream side in the flow direction of the reaction gas, of theat least two of the unit cells may be greater than the length of thereaction gas passage provided in each of those, on the upstream side inthe flow direction of the reaction gas, of the at least two of the unitcells. With this configuration, there occurs a pressure drop of thereaction gas on the downstream side in the flow direction of thereaction gas, so that it is possible to improve the drainagecharacteristic of produced water.

[0015] Further those, provided in the at least two of the unit cells, ofthe reaction gas passages may have shapes different from each other. Forexample, by forming the reaction gas passage on the upstream side in theflow direction into a linear shape and forming the reaction gas passageon the downstream side in the flow direction into a meandering shape, itis possible to change the length of the reaction gas passages with asimple configuration.

[0016] Further those, provided in the at least two of the unit cells, ofthe unified bodies may be different from each other. For example, theheat resistance of the unified body provided in each of those, on thedownstream side in the flow direction of the reaction gas, of the atleast two of the unit cells may be higher than the heat resistance ofthe unified body provided in each of those, on the upstream side in theflow direction of the reaction gas, of the at least two of the unitcells. This is because the temperature of the unified body on thedownstream side in the flow direction becomes higher than thetemperature of the unified body on the upstream side in the flowdirection. Preferably, the unified body provided in each of those, onthe upstream side in the flow direction of the reaction gas, of the atleast two of the unit cells is provided with a fluorine based membrane;and the unified body provided in each of those, on the downstream sidein the flow direction of the reaction gas, of the at least two of theunit cells is provided with a hydrocarbon based membrane. Since theunified body on the downstream side in the flow direction, which ishigher in temperature than the unified body on the upstream side in theflow direction, is made from a hydrocarbon based membrane having a highheat resistance, the useful life of the unified body on the downstreamside can be prolonged.

[0017] Preferably, each separator is interposed between adjacent two ofthe unified bodies; and the separator has, on its plane, a reaction gassupply communication hole for supplying the reaction gas into thereaction gas passage provided in each of the unit cells and a reactiongas discharge communication hole for discharging the reaction gas fromthe reaction gas passage provided in each of the unit cells. With thisconfiguration, it is possible to improve the drainage characteristic ofproduced water, and to eliminate the need of provision of a special sealmechanism which is required in the case of providing a separate manifoldoutside the cell assembly.

[0018] Preferably, each separator is interposed between adjacent two ofthe unified bodies and the separator is configured as a metal platehaving a shape of projections and depressions corresponding to the shapeof the reaction gas passage. With this configuration, the separator canbe formed of a corrugated metal sheet, and thereby the separator can bethinned.

[0019] Preferably, the separator has, on the side facing to one of theunified bodies, a fuel gas passage functioning as the reaction gaspassage, and also has, on the side facing to the other of the unifiedbodies, an oxidizing gas passage functioning as the reaction gaspassage. With this configuration, the separator structure can be easilythinned as compared with a separator structure in which the fuel gaspassage and an oxidizing gas passage are individually provided on twoseparators. As a result, it is possible to miniaturize the whole cellassembly.

[0020] Preferably, the reaction gas passage is set such that thereaction gas passes through a reaction plane of one of the adjacent twoof the unit cells, flows in the stacking direction of the unit cells,and flows on a reaction plane of the other of the adjacent one of theunit cells. Concretely, the reaction gas passage may be set tomeanderingly extend toward a communication hole opened in the stackingdirection of the unit cells. With these configurations, it is possibleto reduce the length of the passages for communicating the unit cells toeach other, and also to easily form a temperature gradient most suitablefor increasing the power generation performance along the flow directionof the reaction gas.

[0021] The flow direction of a fuel gas passage as the reaction gaspassage along the reaction plane of the unit cell may be opposite to theflow direction of an oxidizing gas passage as the reaction gas passagealong the reaction plane of the unit cell. With this configuration, itis possible to effectively humidify the anode by water produced on thecathode.

[0022] Preferably, fuel gas passages as the reaction gas passages areprovided in series in the plurality of unit cells; and oxidizing gaspassages as the reaction gas passages are provided in parallel in theplurality of unit cells. With this configuration, it is possible to givea sufficient pressure drop to the fuel gas passage having a lowviscosity, and hence to effectively discharge water from the anode side.

[0023] Each of a fuel gas passage and an oxidizing gas passage as thereaction gas passages may be provided in such a manner as, to linearlyextend along the reaction plane of the unit cell. With thisconfiguration, since the gas passage has no bent portion, it is possibleto ensure a desirable drainage characteristic, and to easily produce apassage member (separator) from a metal sheet by press-working.

[0024] At least one of a fuel gas passage and an oxidizing gas passageas the reaction gas passages may be provided with a reaction gas inletand a reaction gas outlet on one side of the unit cell in the planedirection. With this configuration a so-called inner manifold isdisposed in the cell assembly, so that the whole cell assembly can beminiaturized.

[0025] Preferably, an intermediate communication hole communicated tothe reaction gas-passage is provided for each of the unit cells in sucha manner as to extend in the stacking direction of the unit cells; andthe reaction gas passages form an approximately U-shaped flow lineextending from one reaction gas inlet of one of the adjacent two of theunit cells to a reaction gas outlet of the other of the adjacent two ofthe unit cells through the intermediate communication holes. With thisconfiguration, it is possible to reduce the length of the passagescommunicating the unit cells to each other, and also to easily form atemperature gradient most suitable for increasing the power generationperformance along the flow direction of the reaction gas.

[0026] Preferably, coolant passages may be provided with the pluralityof the unit cells put therebetween while being located on both sides ofthe unit cells in the stacking direction of the unit cells. With thisconfiguration, it is possible to simplify the cooling structure andhence to easily reduce the size and weight of the whole cell assembly.In particular, the coolant passages may be closer to an oxidizing gaspassage provided in the unit cell on the upstream side in the flowdirection of the oxidizing gas as compared with an oxidizing gas passageprovided in the unit cell on the downstream side in the flow directionof the oxidizing gas. With this configuration, it is possible toincrease the temperature of the unit cell on the downstream side where alarge amount of water tends to accumulate, and hence to reduce arelative humidity in a region from the oxidizing gas inlet to thecathode side outlet.

[0027] Preferably, coolant inlets and coolant outlets communicated tothe coolant passages are provided on one side of the unit cells in theplane direction of the unit cells. With this configuration, since aninternal manifold is formed in the cell assembly, it is possible tominiaturize the whole cell assembly. Further, the coolant passages maybe configured to form an approximately U-shaped flow line for allowingthe coolant to flow from the coolant inlet to one side of a partitionwall member, flow along the one side of the partition wall member, flowto the other side of the partition wall member via an intermediatereturn portion, and flow in the opposite direction along the other sideof the partition wall member. With this configuration, it is possible toreduce the length of the passages for communicating the unit cells toeach other, and also to easily form a temperature gradient most suitablefor increasing the power generation performance along the flow directionof the reaction gas.

[0028] The coolant passage may be provided, in such a manner as tolinearly extend along the plane direction of the unit cell. With thisconfiguration, since the gas passage has no bent portion, it is possibleto ensure a desirable drainage characteristic, and to easily produce apassage member from a metal sheet by press-working.

[0029] According to the present invention, there is provided a solidpolymer electrolyte fuel cell assembly compose of a plurality of unitcells integrally stacked to each other, each of the unit cells having aunified body formed by holding a solid polymer electrolyte membranebetween an anode and a cathode, characterized in that coolant passagescommunicated to each other in series are provided with the plurality ofunit cells put therebetween while being located on both sides of theunit cells in the stacking direction of the unit cells. With thisconfiguration, it is possible to give both an optimum temperaturedistribution and an optimum humidity distribution to the unit cellsstacked to each other.

[0030] According to the present invention, there is provided a fuel cellstack composed of a stack of a plurality of cell assemblies,characterized in that each of the plurality of cell assemblies iscomposed of a plurality of unit cells integrally stacked to each other,each of the unit cells having a unified body formed by holding a solidpolymer electrolyte membrane between an anode and a cathode; andreaction gas passages for allowing at least one of reaction gasescomposed of a fuel gas and an oxidizing gas to flow in the plurality ofunit cells are provided in the cell assembly in such a manner that atleast portions of the reaction gas passages are communicated in seriesto each other over the unit cells.

[0031] With this configuration, in each cell assembly, a reaction gas inan amount required for cell reaction in the unit cell on the upstreamside in the flow direction and the unit cell on the downstream side inthe flow direction is supplied to the unit cell on the upstream side, sothat the flow rate of the reaction gas supplied in the cell assembly isincreased, with a result that it is possible to equalize humidities inthe cell assemblies, and also to equalize current density distributionsin the whole fuel cell stack and hence to reduce a concentrationoverpotential.

[0032] In each cell assembly, at least two of the unit cells may havestructures different from each other. With this configuration, it ispossible to adopt the structure most suitable for reaction in each unitcell. Further, a coolant passage may be provided only between adjacenttwo of the cell assemblies. With this configuration, it is possible tosimplify the coolant passages and hence to easily miniaturize the wholefuel dell stack.

[0033] Preferably, a reaction gas supply communication hole and areaction gas discharge communication hole, which are opened in thestacking direction of the fuel cell stack, are provided; andintermediate communication holes opened in the stacking direction of thefuel cell stack are provided in a flow line between the reaction gassupply communication hole and the reaction gas discharge communicationhole. With this configuration, it is possible to reduce the length ofthe passages for communicating the unit cells to each other, and also toeasily form a temperature gradient most suitable for increasing thepower generation performance along the flow direction of the reactiongas.

[0034] Each of the intermediate communication holes may be provided in aflow line between a reaction gas inlet provided in a plane of one ofadjacent two of the unit cells and a reaction gas outlet provided in aplane of the other of the adjacent two of the unit cells. Theintermediate communication hole may be provided for communicatingadjacent two of the unit cells provided in adjacent two of the cellassemblies to each other. The intermediate communication hole may beprovided for communicating adjacent two of the unit cells only in one ofthe cell assemblies to each other. With these configurations, since theintermediate communication holes are integrally communicated to eachother, it is possible to equalize the concentrations of the reaction gasin the stacking direction of the unit cells.

[0035] According to the present invention, there is provided a fuel cellstack composed of a stack of a plurality of cell assemblies,characterized in that each of the plurality of cell assemblies iscomposed of a plurality of unit cells integrally stacked to each other,each of the unit cells having a unified body formed by holding a solidpolymer electrolyte membrane between an anode and a cathode; and coolantpassages communicated to each other in series are provided with theplurality of unit cells put therebetween while being located on bothsides of the unit cells in the stacking direction of the unit cells.With this configuration, it is possible to give an optimum temperaturedistribution and an optimum humidity distribution to each of the unitcells stacked to each other.

[0036] According to the present invention, there is provided a method ofsupplying a reaction gas to a solid polymer electrolyte fuel cellassembly composed of a plurality of unit cells integrally stacked toeach other, each of the unit cells having a unified body formed byholding a solid polymer electrolyte membrane between an anode and acathode, wherein reaction gas passages for allowing at least one ofreaction gases composed of a fuel gas and an oxidizing gas to flow inthe plurality of unit cells are provided in the cell assembly in such amanner that at least portions of the reaction gas passages arecommunicated in series to each other over the unit cells, the methodbeing characterized by supplying the reaction gas from a reaction gassupply communication hole to a plurality of reaction gas passages in theunit cells in parallel, to subject the reaction gas flowing in thereaction gas passages to cell reaction; and discharging the spentreaction gas to reaction gas discharge communication holes. With thisconfiguration, it is possible to increase the flow rate, flow velocity,and pressure drop of the reaction gas, and hence to effectively improvethe reaction performance of each unit cell.

[0037] Preferably, the reaction gas is introduced in the unit cell onthe upstream side in the flow direction of the reaction gas to be usedfor cell reaction, and is then introduced, via an intermediatecommunication hole, in the unit cell on the downstream side in the flowdirection of the reaction gas to be used for cell reaction. At thistime, the reaction gas in an amount required for reaction in the wholeof the cell assembly may be introduced in the unit cell on the mostupstream side in the flow direction of the reaction gas.

[0038] Preferably, the reaction gas is an oxidizing gas; and a coolantis supplied in coolant passages which are closer to an oxidizing gaspassage provided in the unit cell on the upstream side in the flowdirection of the oxidizing gas as compared with an oxidizing gas passageprovided in the unit cell on the downstream side in the flow directionof the oxidizing gas. With this configuration, it is possible to reducea relative humidity in a region from the oxidizing gas inlet to thecathode side outlet by increasing the temperature of the unit cell onthe downstream side in the flow direction in which a great amount ofwater tends to accumulate.

[0039] The above and other objects, features, and advantages of thepresent invention will become more apparent from the followingdescription when taken in conjunction with the accompanying drawings inwhich preferred embodiments of the present invention are shown by way ofillustrative example.

BRIEF DESCRIPTION OF DRAWINGS

[0040]FIG. 1 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly according to a firstembodiment of the present invention.

[0041]FIG. 2 is a schematic perspective view of a fuel cell stack.

[0042]FIG. 3 is an illustrative view of the cell assembly, with partspartially cutaway.

[0043]FIG. 4 is a front view of a first separator of the cell assembly.

[0044]FIG. 5 is a view showing flows of reaction gases and a coolant inthe cell assembly.

[0045]FIG. 6 is a view illustrating a manner of making cross-sections ofpassages different from each other by making the depths of the passagesdifferent from each other.

[0046]FIG. 7 is a view illustrating a manner of making cross-sections ofpassages different from each other by making the widths of the passagesdifferent from each other.

[0047]FIG. 8 is a view illustrating a manner of making cross-sections ofpassages different from each other by making the number of the passagesdifferent from each other.

[0048]FIG. 9 is an exploded perspective view of the cell assembly inwhich the passage lengths are changed.

[0049]FIG. 10 is an exploded perspective view of a structure of the cellassembly in which intermediates communication holes are communicated toeach other only in each cell.

[0050]FIG. 11 is an exploded perspective view of a structure of the cellassembly in which an intermediate communication holes are provided incentral planes.

[0051]FIG. 12 is a graph illustrating temperatures of cathodes in firstand second unit cells.

[0052]FIG. 13 is a graph illustrating relative humidities of thecathodes in the first and second unit cells.

[0053]FIG. 14 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly according to a secondembodiment of the present invention.

[0054]FIG. 15 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly according to a thirdembodiment of the present invention.

[0055]FIG. 16 is a view showing flows of reaction gases and a coolant inthe cell assembly according to the third embodiment of the presentinvention.

[0056]FIG. 17 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly according to a fourthembodiment of the present invention.

[0057]FIG. 18 is a view showing flows of reaction gases and a coolant inthe cell assembly according to the fourth embodiment of the presentinvention.

[0058]FIG. 19 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly according to a fifthembodiment of the present invention.

[0059]FIG. 20 is a view showing flows of reaction gases and a coolant inthe cell assembly according to the fifth embodiment of the presentinvention.

[0060]FIG. 21 is a diagram showing a symbolized passage configuration ofthe cell assembly according to the first embodiment.

[0061]FIG. 22 is a diagram showing a symbolized passage configuration ofthe cell assembly according to the third embodiment.

[0062]FIG. 23 is a diagram showing a symbolized passage configuration ofthe cell assembly according to the fourth embodiment.

[0063]FIG. 24 is a diagram showing a symbolized passage configuration ofthe cell assembly according to the fifth embodiment.

[0064]FIG. 25 is a diagram showing a typical symbolized passageconfiguration.

[0065]FIG. 26 is a diagram showing another symbolized passageconfiguration.

[0066]FIG. 27 is a diagram showing a further symbolized passageconfiguration.

[0067]FIG. 28 is a diagram showing still a further symbolized passageconfiguration.

[0068]FIG. 29 is a diagram showing a typical passage configuration of athree-cell structure.

[0069]FIG. 30 is a diagram showing another passage configuration of thethree-cell structure.

[0070]FIG. 31 is a diagram showing a typical passage configuration of afour-cell structure.

[0071]FIG. 32 is a diagram showing a passage configuration of athree-cell structure in which a fuel gas side has a merge configuration.

[0072]FIG. 33 is a diagram showing a passage configuration of afour-cell structure in which a fuel gas side has a merge configuration.

[0073]FIG. 34 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly according to a sixthembodiment of the present invention.

[0074]FIG. 35 is a view showing flows of reaction gases and a coolant inthe cell assembly according to the sixth embodiment of the presentinvention.

[0075]FIG. 36 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly according to a seventhembodiment of the present invention.

[0076]FIG. 37 is a view showing flows of reaction gases and a coolant inthe cell assembly according to the seventh embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0077]FIG. 1 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly 10 according to a firstembodiment of the present invention, and FIG. 2 is a schematicperspective view of a fuel cell stack 12 obtained by stacking aplurality of sets of the cell assemblies 10 to each other.

[0078] As shown in FIG. 1, the cell assembly 10 includes a first unitcell 14 and a second unit cell 16 which are stacked to each other. Thefirst unit cell 14 has a first unified body (so-called,“membrane-electrode assembly”) 18, and the second unit cell 16 has asecond unified body 20.

[0079] The first unified body 18 has a solid polymer electrolytemembrane 22 a, and a cathode 24 a and an anode 26 a which are disposedwith the electrolyte membrane 22 a put therebetween, and the secondunified body 20 has a solid polymer electrolyte membrane 22 b, and acathode 24 b and an anode 26 b which are disposed with the electrolytemembrane 22 b put therebetween. Each of the cathodes 24 a and 24 b andthe anodes 26 a and 26 b is formed by joining a noble metal basedcatalyst electrode layer on a base member mainly made from carbon and isprovided, on its surface, with a gas diffusion layer formed of a porouslayer, for example, a porous carbon paper.

[0080] As shown in FIGS. 1 and 3, a first separator 28 is disposed onthe cathode 24 a side of the first unified body 18; a second separator30 is disposed on the anode 26 b side of the second unified body 20; andan intermediate separator 32 is disposed between the first and secondunified bodies 18 and 20. A thin wall plate (partition wall member) 34is provided on each of both outer surface sides of the first and secondseparators 28 and 30.

[0081] As shown in FIG. 1, each of the first and second unified bodies18 and 20, the first and second separators 28 and 30, and theintermediate separator 32 has, at its one edge portion in the long-sidedirection, an oxidizing gas inlet 36 a, an oxidizing gas outlet 36 b,and a fuel gas intermediate communication hole 38. The oxidizing gasinlet 36 a, which is also called a reaction gas supplying communicationhole and the oxidizing gas outlet 36 b, which is also called a reactiongas discharging communication hole, are adapted to allow an oxidizinggas (reaction gas) such as an oxygen containing gas or air to passthrough; and the fuel gas intermediate communication hole 38 is adaptedto allow a fuel gas (reaction gas) such as a hydrogen containing gas topass therethrough. These oxidizing gas inlets 36 a (oxidizing gasoutlets 36 b, fuel gas intermediate communication holes 38) formed inrespective cell components 18, 20, 28, 30, and 32 are communicated toeach other in the stacking direction (shown by an arrow A) of the firstand second unit cells 14 and 16.

[0082] On the other hand, each of the first and second unified bodies 18and 20, the first and second separators 28 and 30, and the intermediateseparator 32 has, at its the other edge portion in the long-sidedirection, an oxidizing gas intermediate communication hole 40, a fuelgas inlet 42 a, a fuel gas outlet 42 b, a coolant inlet 44 a, and acoolant outlet 44 b. The oxidizing gas intermediate communication hole40 is adapted to allow an oxidizing gas to pass therethrough; the fuelgas inlet 42 a, which is also called a reaction gas supplyingcommunication hole, and the fuel gas outlet 42 b, which is also called areaction gas discharging communication hole, are adapted to allow a fuelgas to pass therethrough; and the coolant inlet 44 a and the coolantoutlet 44 b are adapted to allow a coolant to pass therethrough. Theseoxidizing gas intermediate communication holes 40 (fuel gas inlets 42 a,fuel gas outlets 42 b, coolant inlets 44 a, coolant outlets 44 b) formedin respective cell components 18, 20, 28, 30, and 32 are communicated toeach other in the direction shown by the arrow A.

[0083] The first separator 28 is configured as a metal sheet. A portion,facing to a reaction plane (power generation plane) of the first unifiedbody 18, of the metal sheet is formed into a shape of projections anddepressions, for example, into a corrugated shape. To be more specific,as shown in FIGS. 3 and 4, the first separator 28 has, on the sidefacing to the cathode 24 a of the first unified body 18, a plurality ofoxidizing gas passages (reaction gas passages) 46 provided by forming,as described above, the side facing to the cathode 24 a, of the firstseparator 28 into a corrugated shape. The oxidizing gas passages 46linearly extend in the long-side direction (shown by an arrow B). Theone-ends of the oxidizing gas passages 46 are communicated to theoxidizing gas inlet 36 a and the other ends thereof are communicated tothe oxidizing gas intermediate communication hole 40.

[0084] As shown in FIGS. 1 and 3, the first separator 28 also has, onthe side facing to one surface of the wall plate 34, a plurality ofcoolant passages 48. The coolant passages 48 linearly extend in thelong-side direction (shown by the arrow B). The one-ends of the coolantpassages 48 are communicated to the coolant inlet 44 a, and the otherends thereof are communicated to the coolant outlet 44 b by way of theother surface side of the wall plate 34 through a hole portion 50 as anintermediate return portion formed in the wall plate 34 or in a separatemember.

[0085] The second separator 30 has a configuration which issubstantially similar to that of the first separator 28. The secondseparator 30 has, on the side facing to the anode 26 b of the secondunified body 20, a plurality of fuel gas passages (reaction gaspassages) 52. The fuel gas passages 52 linearly extend in the long-sidedirection (shown by the arrow B). The one-ends of the fuel gas passages52 are communicated to the fuel gas intermediate communication hole 38and the other ends thereof are communicated to the fuel gas outlet 42 b.The second separator 30 also has, on the side facing to the wall plate34 of the next cell assembly 10, a plurality of coolant passages 54. Thecoolant passages 54 linearly extend in the long-side direction (shown bythe arrow B), with their terminals communicated to the coolant outlet 44b.

[0086] The intermediate separator 32 has a configuration which issubstantially similar to that of each of the first and second separators28 and 30. The intermediate separator 32 has, on the side facing to theanode 26 a of the first unified body 18, a plurality of fuel gaspassages (reaction gas passages) 56. The fuel gas passages 56 linearlyextend in the long-side direction (shown by the arrow B). The one-endsof the fuel gas passages 56 are communicated to the fuel gas inlet 42 aand the other ends thereof are communicated the fuel gas intermediatecommunication hole 38.

[0087] As shown in FIG. 3, the intermediate separator 32 also has, onthe side facing to the cathode 24 b of the second unified body 20, aplurality of oxidizing gas passages (reaction gas passages) 58. Theoxidizing gas passages 58 linearly extend in the long-side direction(shown by the arrow B). The one-ends of the oxidizing gas passages 58are communicated to the oxidizing gas intermediate communication hole 40and the other ends thereof are communicated to the oxidizing gas outlet36 b.

[0088] The oxidizing gas passage's 46 provided in the first unit cell 14and the oxidizing gas passages 58 provided in the second unit cell 16,which are communicated in series to each other, are different from eachother in passage cross-section; and the fuel gas passages 56 provided inthe first unit cell 14 and the fuel gas passages 52 provided in thesecond unit cell 16, which are communicated in series to each other, aredifferent from each other in passage cross-section. As shown in FIG. 3,the passage cross-section of the oxidizing gas passage 58 on the outletside is smaller than that of the oxidizing gas passage 46 on the inletside; and the passage cross-section of the fuel gas passage 52 on theoutlet side is smaller than that of the fuel gas passage 56 on the inletside.

[0089] A specific number of sets of the cell assemblies 10 configured asdescribed above are, as shown in FIG. 2, stacked to each other in thedirection shown by the arrow A by means of fixing means (not shown). Endplates 62 a and 62 b are disposed, via terminal electrodes 60 a and 60b, on both ends of the sets of the cell assemblies 10 in the directionshown by the arrow A, followed by fastening of the end plates 62 a and62 b by means of tie rods (not shown) or the like, to obtain a fuel cellstack 12.

[0090] The end plate 62 a has, at one edge portion in the long-sidedirection, an oxidizing gas supply port 64 a communicated to theoxidizing gas inlets 36 a, an oxidizing gas discharge port 64 bcommunicated to the oxidizing gas outlets 36 b. The end plate 62 a alsohas, on the other edge portion in the long-side direction, a fuel gassupply port 66 a communicated to the fuel gas inlets 42 a, a fuel gasdischarge port 66 b communicated to the fuel gas outlets 42 b, a coolantsupply port 68 a communicated to the coolant inlets 44 a, and a coolantdischarge port 68 b communicated to the coolant outlets 44 b.

[0091] The operations of the fuel cell stack 12 and the cell assembly 10configured as described above will be described below.

[0092] In the fuel cell stack 12, a fuel gas such as a hydrogencontaining gas is supplied from the fuel gas supply port 66 a; anoxidizing gas such as air or an oxygen containing gas is supplied fromthe oxidizing gas supply port 64 a; and a coolant such as pure water,ethylene glycol, or oil is supplied from the coolant supply port 68 a,so that the fuel gas, oxidizing gas, and coolant are sequentiallysupplied to the plurality of cell assemblies 10 stacked to each other inthe direction shown by the arrow A.

[0093] As shown in FIG. 5, the oxidizing gas supplied to the oxidizinggas inlets 36 a communicated to each other in the direction shown by thearrow A is introduced in the plurality of oxidizing gas passages 46provided in the first separator 28 and is moved along the cathode 24 aof the first unified body 18, whereas the fuel gas supplied to the fuelgas inlets 42 a communicated to each other in the direction shown by thearrow A is introduced in the plurality of fuel gas passages 56 providedin the intermediate separator 32 and is moved along the anode 26 a ofthe first unified body 18. Accordingly, in the first unified body 18,the oxidizing gas supplied to the cathode 24 a and the fuel gas suppliedto the anode 26 a are consumed by electrochemical reaction in thecatalyst layers of the electrodes, to result in power generation.

[0094] The oxidizing gas, part of which has been consumed in the firstunified body 18, is introduced from the oxidizing gas passages 46 intothe oxidizing gas intermediate communication hole 40 of the firstunified body 18, being moved in the direction shown by the arrow Athrough the oxidizing gas intermediate communication hole 40 of theintermediate separator 32, and is introduced in the oxidizing gaspassages 58 provided in the intermediate separator 32. The oxidizing gasthus introduced in the oxidizing gas passages 58 is then moved along thecathode 24 b of the second unified body 20.

[0095] Similarly, the fuel gas, part of which has been consumed in theanode 26 a of the first unified body 18, is introduced into the fuel gasintermediate communication hole 38 of the intermediate separator 32,being moved in the direction shown by the arrow A through the fuel gasintermediate communication hole 38 of the second unified body 20, and isintroduced in the fuel gas passages 52 provided in the second separator30. The fuel gas thus introduced in the fuel gas passages 52 is thenmoved along the anode 26 b of the second unified body 20. Accordingly,in the second unified body 20, the oxidizing gas and fuel gas areconsumed by electrochemical reaction in the catalyst layers of theelectrodes, to result in power generation. The oxidizing gas with itsoxygen having been consumed is discharged into the oxygen gas outlet 36b of the second separator 30, and the fuel gas with its hydrogen havingbeen consumed is discharged into the fuel gas outlet 42 b of the secondseparator 30.

[0096] On the other hand, the coolant flowing through the coolant inlets44 a communicated to each other in the direction shown by the arrow Areaches the first separator 28. The coolant is then moved along thecoolant passages 48 provided in the first separator 28, being returnedfrom the hole portion 50 formed in the wall plate 34 and moved along thecoolant passages 54 provided in the second separator 30 of the next cellassembly 10, and is discharged into the coolant outlet 44 b of thesecond separator 30.

[0097] According to the first embodiment, the cell assembly 10 isconfigured as one body of the first and second unit cells 14 and 16, andfurther, at least part of the oxidizing gas passages 46 provided in thefirst unit cell 14 are communicated in series to at least part of theoxidizing gas passages 58 provided in the second unit cell 16 via theoxidizing gas intermediate communication holes 40, whereas at least partof the fuel gas passages 56 provided in the first unit cell 14 iscommunicated in series to at least part of the fuel gas passage 52provided in the second unit cell 16 via the fuel gas intermediatecommunication holes 38. Accordingly, the oxidizing gas in an amount offlow required for the whole reaction in the first and second unit cells14 and 16 is supplied to the oxidizing gas passages 46 on the inletside, whereas the fuel gas in an amount of flow required for the wholereaction in the first and second unit cells 14 and 16 is supplied to thefuel gas passages 56 on the inlet side. In other words, the oxidizinggas in an amount of flow being twice the amounts of flow generallyrequired for the reaction in the unit cell is supplied to the oxidizinggas passages 46 on the inlet side, whereas the fuel gas in an amount offlow being twice the amount of flow generally required for the reactionin the unit cell is supplied to the fuel gas passages 56 on the inletside.

[0098] As a result, particularly, drainage characteristics of theoxidizing gas passages 46 and 58 in which water is produced areimproved, and thereby humidities in the oxidizing gas passages 46 and 58in the first and second unit cells 14 and 16 are equalized. This iseffective to equalize current density distributions in the first andsecond unit cells 14 and 16 and hence to reduce occurrence of aconcentration overpotential.

[0099] Since the oxidizing gas passages 46 in the first unit cell 14 arecommunicated in series to the oxidizing gas passages 58 in the secondunit cell 16 and the fuel gas passages 56 in the first unit cell 14 arecommunicated in series to the fuel gas passages 52 in the second unitcell 16, the flow velocity of the oxidizing gas supplied to theoxidizing gas inlets 36 a and also the flow velocity of the fuel gassupplied to the fuel gas inlets 42 a become high as compared with theconventional unit cell structure. As a result, it is possible toeffectively discharge water produced in the first and second unit cells,and hence to significantly improve the whole drainage characteristic ofthe cell assembly 10.

[0100] Since the oxidizing gas passages 46 in the first unit cell 14 arecommunicated in series to the oxidizing gas passages 58 in the secondunit cell 16, to form a long oxidizing gas (reaction gas) path extendingfrom the first unit cell 14 to the second unit cell 16, whereas the fuelgas passages 56 in the first unit cell 14 are communicated in series tothe fuel gas passages 52 in the second unit cell 16, to form a long fuelgas (reaction gas) path extending from the first unit cell 14 to thesecond unit cell 16, there can be obtained advantages of increasing apressure drop in the first and second unit cells 14 and 16 therebyeffectively improving the drainage characteristics of water produced bythe oxidizing gas and fuel gas in the first and second unit cells 14 and16, and of the equalizing distributions of the oxidizing gas and fuelgas to respective cell assemblies 10 in the fuel cell stack 12.

[0101] According to the first embodiment, since the passagecross-section of each oxidizing gas passage 46 is different from that ofeach oxidizing gas passage 58, whereas the passage cross-section of eachfuel gas passage 56 is different from that of each fuel gas passage 52.To be more specific, as shown in FIG. 3, the passage cross-section ofthe oxidizing gas passage 58 on the outlet side is smaller than that ofthe oxidizing gas passage 46 on the inlet side, whereas the passagecross-section of the fuel gas passage 52 on the outlet side is smallerthan that of the fuel gas passage 56 on the inlet side. Along withmovement of each of the oxidizing gas and the fuel gas toward the outletside, the amount of the gas is reduced by consumption due to cellreaction. From this viewpoint, by making the passage cross-section ofeach of the oxidizing gas passages 58 and the fuel gas passages 52 onthe outlet side smaller, the reactions on the reaction plane of thesecond unified body 20 can be equalized.

[0102] The passage cross-section of each of the oxidizing gas passages46 can be made different from that of each of the oxidizing gas passages58 by changing the passage depth, the passage width, or the number ofthe passages, and similarly, the passage cross-section of each of thefuel gas passages 56 can be made different from that of each of the fuelgas passages 52 by changing the passage depth, the passage width, or thenumber of the passages as follows.

[0103] In an example shown in FIG. 6, the passage depth of eachoxidizing gas passage 58 a provided in a plate-like intermediateseparator 32 a is set to be smaller than the passage depth of eachoxidizing gas passage 46 a provided in a plate-like first separator 28a, whereas the passage depth of each fuel gas passage 52 a provided in aplate-like second separator 30 a is set to be smaller than the passagedepth of each fuel gas passage 56 a provided in the plate-likeintermediate separator 32 a. With this configuration, as the additionaleffect, each of the first and second unit cells 14 and 16 can be thinnedand thereby the whole cell assembly 10 can be easily miniaturized.

[0104] In an example shown in FIG. 7, the passage width of each outletside oxidizing gas passage 58 b formed in a plate-like intermediateseparator 32 b is smaller than the passage width of each inlet sideoxidizing gas passage 46 b formed in a plate-like first separator 28 b,and similarly, the passage width of an outlet side fuel gas passage 52 bformed in a plate-like second separator 30 b is smaller than the passagewidth of an inlet side fuel gas passage 56 b formed in the intermediateseparator 32 b. With this configuration, as the additional effect, thecontact area between the first and second unit cells 14 and 16 isincreased, thereby reducing the contact resistance.

[0105] In an example shown in FIG. 8, the number of an outlet sideoxidizing gas passages 58 c provided in a plate-like intermediateseparator 32 c is smaller than the number of an inlet side oxidizing gaspassages 46 c provided in a plate-like first separator 28 c, andsimilarly, the number of an outlet side fuel gas passages 52 c providedin a plate-like second separator 30 c is smaller than the number of aninlet side fuel gas passages 56 c provided in the intermediate separator32 c. With this configuration, as the additional effect, the contactarea between the first and second unit cells 14 and 16 can beeffectively increased.

[0106] Further, to improve the drainage characteristics in the first andsecond unit cells 14 and 16, the gas passage length in the second unitcell 16 on the outlet side may be set to be greater than the gas passagelength in the first unit cell 14 on the inlet side. Since the amount ofproduced water becomes larger on the outlet side, the drainagecharacteristic of the produced water can be improved by making the gaspassage length on the outlet side greater, thereby generating a pressuredrop on the outlet side.

[0107] To be more specific, as shown in FIG. 9, fuel gas passages 56 areprovided in an intermediate separator 32 in such a manner as to linearlyextend, while fuel gas passages 52 d are provided in a second separator30 d in such a manner as to meanderingly extend. Accordingly, the gaspassage length of the fuel gas passages 52 d on the outlet side iseffectively greater than the gas passage length of the fuel gas passages56 on the inlet side. In addition, the meandering fuel gas passages 52 dmay be replaced with bent or curved fuel gas passages.

[0108] In the first embodiment, since the cell assembly 10 is formed ofan integral body of a plurality of unit cells, for example, the two unitcells 14 and 16, it is possible to effectively simplify the workabilityat the time of assembly of the fuel cell stack 12 by stacking the cellassemblies 10 to each other, as compared with the assembly of theconventional fuel cell stack by stacking units cells to each other.

[0109] Further, the miniaturization of each cell assembly 10 easilyleads to miniaturization of the whole fuel cell stack 12. With respectto miniaturization of the cell assembly 10, since each of the first andsecond separators 28 and 30 and the intermediate separator 32 is formedof the metal sheet formed into a corrugated shape (shape of projectionsand depressions), the separator can be thinned, with a result that thewhole cell assembly 10 can be also thinned.

[0110] In the first embodiment, the intermediate separator 32 has, onthe side facing to the first unified body 18, the fuel gas passages 56and also has, on the side facing to the second unified body 20, theoxidizing gas passages 58 (see FIG. 3). Accordingly, the structure ofthe intermediate separator 32 becomes thinner than that of a structurein which the fuel gas passages 56 and the oxidizing gas passages 58 areindividually provided in two separators. This makes it possible tominiaturize the whole cell assembly 10.

[0111] Since each of the first and second separators 28 and 30 and theintermediate separator 32 has the oxidizing gas inlets 36 a, oxidizinggas outlets 36 b, fuel gas inlets 42 a, and fuel gas outlets 42 brespectively communicated to each other in the stacking direction of thefirst and second unit cells 14 and 16, it is possible to eliminate theneed of provision of a separate manifold (external manifold) outside thecell assembly 10 and thereby also eliminate the need of provision of aseal structure at an end portion of the external manifold in thestacking direction of the units cells, and hence to miniaturize the cellassembly 10 and simplify the configuration thereof.

[0112] In the first embodiment, as shown in FIG. 5, the reaction gas,for example, the oxidizing gas flows along the cathode 24 a of the firstunified body 18 via the oxidizing gas passages 46, being moved in thedirection shown by the arrow A (stacking direction) via the oxidizinggas intermediate communication holes 40, and flows along the cathode 24b of the second unified body 20 via the oxidizing gas passages 58.

[0113] Accordingly, since the oxidizing gas meanderingly flows along theoxidizing gas passages toward the oxidizing gas intermediatecommunication hole for allowing the oxidizing gas to flow in thestacking direction of the first and second unit cells 14 and 16, it ispossible to obtain advantages that the length of the passage throughwhich the first and second unit cells 14 and 16 are communicated to eachother is reduced and also the temperature gradient is easier to beformed along the flow direction of the oxidizing gas (fuel gas).Further, since the fuel gas and the oxidizing gas flow in the directionsopposite to each other along the reaction planes of the first and secondunified bodies 18 and 20, it is possible to desirably humidify theanodes 26 a and 26 b by water produced from the cathodes 24 a and 24 b.

[0114] Further, in the first embodiment, since any coolant passage isnot provided between the first and second unit cells 14 and 16, thetemperature of the second unit cell 16 on the outlet side becomes higherthan that of the first unit cell 14 on the inlet side, with a resultthat the drainage characteristic of produced water can be improved.

[0115] By making the temperature in the gas passages on the second unitcell 16 side higher than that on the first unit cell 14 side as shown inFIG. 12, a relative humidity in the gas passages is changed between thefirst and second unit cells 14 and 16 as shown in FIG. 13. In the firstunit cell 14, a change in humidity is reduced because the oxidizing gasin an amount required for reaction in the first and second unit cells 14and 16 is supplied to the first unit cell 14, and in the second unitcell 16, a change in humidity is also reduced because the temperature ofthe second unit cell 16 is raised.

[0116] With this configuration since the relative humidities in thefirst, and second unit cells 14 and 16 are equalized, it is possible toimprove the ion conductivity of each of the electrolyte membranes 22 aand 22 b and hence to reduce the concentration overpotential.

[0117] By the way, according to the first embodiment, the oxidizing gasintermediate communication holes 40 are provided between the oxidizinggas inlets 36 a and the oxidizing gas outlets 36 b, and the fuel gasintermediate communication holes 38 are provided between the fuel gasinlets 42 a and the fuel gas outlets 42 b.

[0118] The oxidizing gas intermediate communication holes 40 and thefuel gas intermediate communication holes 38 are respectively providedin such a manner as to pass through the first and second unit cells 14and 16 in the direction shown by the arrow A. However, unlike such astructure of the first embodiment, there may be adopted a structureshown in FIG. 10 in which each of the first and second separators 28 and30 has no oxidizing gas intermediate communication hole 40 and no fuelgas intermediate communication hole 38. In this case, only in each cellof the cell assembly 10, the oxidizing gas intermediate communicationholes 40 allow the oxidizing gas to flow therethrough in the directionshown by the arrow A and the fuel gas intermediate communication holes38 allows the fuel gas to flow therethrough in the direction shown bythe arrow A.

[0119] Further, as shown in FIG. 11, an oxidizing gas intermediatecommunication hole 40 a and a fuel gas intermediate communication hole38 a may be provided in a central plane of each of the first and secondseparators 28 and 30 and the intermediate separator 32.

[0120] Next, methods of supplying reaction gases in the cell assembly 10and in the fuel cell stack 12 composed of the stack of the cellassemblies 10 according to the present invention will be describedbelow. It is to be noted that the gas supply is basically performed inaccordance with the above-described operations of the cell assembly 10and the fuel cell stack 12, and therefore, only the features of the gassupply methods will be briefly described.

[0121] As shown in FIG. 5, an oxidizing gas and a fuel gas are suppliedin parallel to the plurality of oxidizing gas passages 46 and theplurality of fuel gas passages 56 from the oxidizing gas inlets 36 a andthe fuel gas inlets 42 a as the reaction gas supply passages provided inthe stacking direction shown by the arrow A of the first and second unitcells 14 and 16. Accordingly, the spent oxidizing gas and fuel gas,which have been used for reaction at the first and second unified bodies18 and 20, are discharged from the oxidizing gas outlets 36 b and thefuel gas outlets 42 b as the reaction gas discharge passages provided inthe direction shown by the arrow A.

[0122] In this case, in the cell assembly 10, the oxidizing gas and fuelgas are introduced in the first unit cell 14 on the upstream side to beused for reaction, and then introduced in the second unit cell 16 on thedownstream side via the oxidizing gas intermediate communication holes40 and the fuel gas intermediate communication holes 38. As a result,the flow rate flow velocity, and pressure drop of each of the oxidizinggas and fuel gas can be increased, so that the reaction performances ofthe first and second unit cells 14 and 16 can be effectively improved.

[0123] Here, each of the oxidizing gas and fuel gas in an amountrequired to be used in the whole cell assembly 10, that is, in amountrequired for reaction in the first and second unit cells 14 and 16, isintroduced in the first unit cell 14 on the upstream side in the flowdirection of the reaction gas.

[0124]FIG. 14 is an exploded perspective view of an essential portion ofa cell assembly 80 according to a second embodiment of the presentinvention. In the cell assembly 80 according to this embodiment, partscorresponding to those in the cell assembly 10 according to the firstembodiment are designated by the same reference numerals and theoverlapped description thereof is omitted. The same is true for thefollowing third and later embodiments.

[0125] The cell assembly 80 includes a first unified body 82 and asecond unified body 84. The first unified body 82 has a fluorine basedelectrolyte membrane 86, and the second unified body 84 has ahydrocarbon based electrolyte membrane 88.

[0126] According to the second embodiment configured as described above,since the temperature of the second unified body 84 on the downstreamside of the flow direction of a reaction gas is higher than that of thefirst unified body 82 on the upstream side in the flow direction of thereaction gas, the hydrocarbon based electrolyte membrane 88 having ahigh heat resistance is provided in the second unified body 84. Withthis configuration, the useful life of the second unified body 84 can beimproved. As a result, since the second unified body 84 can be used fora long period of time, it is possible to enhance the economical merit ofthe cell assembly 80.

[0127]FIG. 15 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly 140 according to a thirdembodiment of the present invention.

[0128] The cell assembly 140 includes a first unit cell 142 and a secondunit cell 144 which are stacked to each other. The first unit cell 142has a first unified body 146, and the second unit cell 144 has a secondunified body 148. The first unified body 146 is held between a firstseparator 150 and a first intermediate separator 154, and the secondunified body 148 is held between a second intermediate separator 156 anda second separator 152. A baffle plate 158 is interposed between thefirst and second intermediate separators 154 and 156.

[0129] The cell assembly 140 has, on one edge portion in the long-sidedirection, fuel gas inlets 42 a, oxidizing gas intermediatecommunication holes 40, and fuel gas outlets 42 b. The fuel gas inlets42 a (oxidizing gas intermediate communication holes 40, fuel gasoutlets 42 b) are communicated to each other in the direction shown byan arrow A. The cell assembly 140 also has, on the other edge portion inthe long-side direction, oxidizing gas inlets 36 a, coolant inlets 44 a,fuel gas intermediate communication holes 38, coolant outlets 44 b, andoxidizing gas outlets 36 b. The oxidizing gas inlets 36 a (coolantinlets 44 a, fuel gas intermediate communication holes 38, coolantoutlets 44 b, oxidizing gas outlets 36 b) are communicated to each otherin the direction shown by the arrow A.

[0130] Coolant passages 54 are provided on a surface, facing to thebaffle plate 158, of each of the first and second intermediateseparators 154 and 156 in such a manner as to linearly extend. One-endsof the coolant passages 54 provided in the first intermediate separator154 are communicated to the coolant inlet 44 a of the first intermediateseparator 154, and the other ends of the coolant passages 54 provided inthe first intermediate separator 154 are returned from the baffle plate158 and are communicated to the coolant passages 54 provided in thesecond intermediate separator 156. The coolant passages 54 provided inthe second intermediate separator 156 are communicated to the coolantoutlet 44 b provided in the second intermediate separator 156.

[0131] In the cell assembly 140 configured as described above, anoxidizing gas, a fuel gas, and a coolant are supplied in series to thefirst and second unit cells 142 and 144 along the flow direction shownin FIG. 16. At this time, the coolant passages 54 are formed between thefirst and second unit cells 142 and 144 via the baffle plate 158. As aresult, in particular, it is possible to prevent the temperature in thecell assembly 140 from being excessively raised.

[0132]FIG. 17 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly 160 according to a fourthembodiment of the present invention. In the cell assembly 160 accordingto the fourth embodiment, parts corresponding to those in the cellassembly 140 according to the third embodiment shown in FIG. 15 aredesignated by the same reference numerals and the overlapped descriptionthereof is omitted.

[0133] The cell assembly 160, which includes a first unit cell 162 and asecond unit cell 164 which are stacked to each other in the directionshown by an arrow A, is characterized in that the oxidizing gasintermediate communication holes 40 provided in the cell assembly 140shown in FIG. 15 are not provided. Accordingly, in the cell assembly160, as shown in FIG. 18, a fuel gas flows along fuel gas passages 56and 52, which are provided in the first and second unit cells 162 and164 respectively in such a manner as to be communicated in series toeach other, and an oxidizing gas flows along oxidizing gas passages 46and 58, which are provided in the first and second unit cells 162 and164 in such a manner as to be individually, that is, in parallel to eachother. That is to say, the fuel gas is supplied to the first and secondunit cells 162 and 164 in series, and the oxidizing gas is supplied tothe first and second unit cells 162 and 164 in parallel.

[0134] In this embodiment, since the fuel gas having a low viscosityflows along the fuel gas passages 56 and 52 communicated to each otherin series, the whole length of the fuel gas passages becomes greater, tothereby give a sufficient pressure drop, with a result that producedwater can be effectively discharged from anodes 26 a and 26 b facing tothe fuel gas passages 56 and 52.

[0135]FIG. 19 is an exploded perspective view of an essential portion ofa solid polymer electrolyte fuel cell assembly 180 according to a fifthembodiment of the present invention, and FIG. 20 is a view showing flowsof an oxidizing gas, a fuel gas, and a coolant in the cell assembly 180.In the cell assembly 180 according to the fifth embodiment, partscorresponding to those in the cell assembly 140 according to the thirdembodiment shown in FIG. 15 are designated by the same referencenumerals and the overlapped description thereof is omitted.

[0136] The cell assembly 180 includes a first unit cell 182 and a secondunit cell 184 which are stacked to each other in the direction shown byan arrow A. The cell assembly 180 has, on a one-edge portion in thelong-side direction, fuel gas inlets 42 a, oxidizing gas intermediatecommunication holes 40, fuel gas outlets 42 b, and coolant intermediatecommunication holes 186.

[0137] In the cell assembly configured as described above, as shown inFIG. 20, a coolant flows through the coolant inlets 44 a in thedirection shown by an arrow A to be introduced between first and secondintermediate separators 154 and 156, and is moved along coolant passages54 provided in the second intermediate separator 156 in the planedirection shown by an arrow B. The coolant is then introduced to acoolant intermediate communication hole 186 provided in a one-edgeportion in the long-side direction of the second intermediate separator156, and moved in the direction shown by the arrow A; and is introducedfrom a coolant intermediate communication hole 186 provided in thesecond intermediate separator 156 to a surface, opposed to the sideoxidizing gas passages 58 are provided, of the second separator 152, andis returned, that is, discharged in the coolant outlet 44 b of thesecond separator 152.

[0138] By the way, the passage configuration of the cell assembly 10according to the first embodiment can be symbolized as shown in FIG. 21.In this figure, the first and second unit cells 14 and 16 constitutingthe cell assembly 10 are designated by CA and CB respectively, and thepassages of the oxidizing gas, fuel gas, and coolant are expressed byR1, R2, and R3, respectively.

[0139] Similarly, the passage configuration of the cell assembly 140according to the third embodiment can be symbolized as shown in FIG. 22;the passage configuration of the cell assembly 160 according to thefourth embodiment can be symbolized as shown in FIG. 23; and the passageconfiguration of the cell assembly 180 according to the fifth embodimentcan be symbolized, as shown in FIG. 24. Accordingly, various kinds ofdifferent passage configurations can be obtained by selectivelycombining the passage configurations shown in FIGS. 21 to 24 with eachother.

[0140] Next, typical combinations of passage configurations will bedescribed with reference to the drawings. It is to be noted that thepassages R1, R2 and R3 can be variously changed by reversing the flowdirection of the passages or changing the positions of the passages onthe right or left side to positions on the left or right side andtherefore, the description of such variations is omitted, and that inthe following passage combinations, only the combinations of theoxidizing gas passages R1 and the coolant passages R3 are shown and thedescription of the configuration the fuel gas passages R2 is omittedbecause the configurations of the fuel gas passages R2 can be variouslyincorporated in the combinations of the oxidizing gas passages R1 andthe coolant passages R3.

[0141]FIG. 25 shows a passage configuration in which the oxidizing gaspassage R1 extends in series from the cell CA to the cell CB, and thecoolant passage R3 extends along a U-shaped line from a portion betweenthe cells CA and CB to the outside of the cell CB. With thisconfiguration, in the cells CA and CB, the temperature becomes highertoward oxidizing gas outlets in the plane direction, so that thehumidities in the cells CA and CB are equalized and also the temperatureof the cell CB on the outlet side becomes higher in the stackingdirection of the cells CA and CB, with a result that the humidities inthe whole cell assembly can be equalized.

[0142] Since the oxidizing gas flows in series from the cell CA side tothe cell CB side, the flow rate per unit cell of the oxidizing gas inthe cell CA is increased, so that the humidities along the planedirection of the cell CA are equalized, and further the drainagecharacteristic is improved due to an increase in flow rate of theoxidizing gas and the distributions of the oxidizing gas and fuel gasinto the cells CA and CB are equalized due to an increase in pressuredrop. Further, since the coolant flows in series and is returned in theU-shape, the flow rate per unit cell of the coolant becomes large, sothat the temperature rise along the plane direction of the cells CA andCB can be reduced and also the humidities in the cells CA and CB can beequalized.

[0143]FIG. 26 shows a passage configuration in which the oxidizing gaspassage R1 extends along a U-shape line, from the cell CA to the cell CBand the coolant passage R3 extends along a U-shape line between thecells CA and CB. With this configuration, the, same effects as thoseobtained by the passage configuration shown in FIG. 25 can be obtained.

[0144]FIG. 27 shows a passage configuration in which the oxidizing gaspassage R1 extends in series from the cell CA side to the cell CB sideand the coolant passage R3 extends in series along; a U-shape betweenthe cell CA side to the cell CB side. With this configuration, the sameeffects as those obtained by the passage configuration shown in FIG. 25can be obtained.

[0145]FIG. 28 shows a passage configuration in which the oxidizing gaspassage R1 extends in a series along a U-shape from the cell CB side tothe cell CA side and the coolant passages R3 extend, between the cellsCA and CB and outside the cell CB, along U-shapes opposite to theU-shape of the oxidizing gas passage R1. With this configuration, thesame effects as those obtained by the passage configuration shown inFIG. 25 can be obtained.

[0146] Even in a three-cell structure, the flow directions of theoxidizing gas, fuel gas, and coolant can be variously changed, like theabove-described two-cell structure.

[0147]FIG. 29 shows a passage configuration of a three-cell structurehaving cells CA, CB and CC. In this passage configuration, the oxidizinggas passage R1 extends in series from the cell CA to the cell CC via thecell CB, and the fuel gas passage R2 extends, in the direction oppositeto the flow direction of the oxidizing gas passage R1, in series fromthe cell CA to the cell CC via the cell CB. In addition, the coolantpassage R3 is provided between the cells CA and CB.

[0148] In such a passage configuration, since the flow rate per unitcell of each of the oxidizing gas and fuel gas is increased, the flowvelocity and pressure drop thereof are improved and partial pressures ofsteam in the cells CA, CB and CC are equalized. Further, since theoxidizing gas and fuel gas oppositely flow along the plane direction inthe cells CA, CB and CC, water produced on the outlet side of theoxidizing gas passage R1 is reversely diffused in the fuel gas passageR2 via the electrolyte membrane, to effectively humidify the fuel gas,thereby improving the self-humidification characteristic.

[0149]FIG. 30 shows a passage configuration of a three-cell structure,in which the oxidizing gas passage R1 extends in series from the cell CCto the cell CA via the cell CB and the fuel gas passage R2 extends inseries from the cell CA to the cell CC via the cell CB; and the coolantpassage R3 meanderingly extends in series from the cell CC to the cellCA via the cell CB.

[0150]FIG. 31 shows a passage configuration of a four-cell structurehaving cells CA, CB, CC and CD. In this passage configuration, theoxidizing gas passage R1 extends in series in the order of the cells CA,CB, CC and CD and the fuel gas passage R2 extends, in the directionopposite to the flow direction of the oxidizing gas passage R1, inseries in the order of the cells CA, CB, CC and CD; and the coolantpassage R3 extends in the direction opposite to the flow direction ofthe oxidizing gas passage R1, in series between the cells CA and CBbetween CB and CC, and between CC and CD.

[0151] With this configuration, since the flow rate per unit cell ofeach of the oxidizing gas and fuel gas is increased, the flow velocityand pressure drop thereof are improved and partial pressures of steam inthe cells CA, CB, CC and CD are equalized.

[0152]FIG. 32 shows a passage configuration of a three-cell structure inwhich the fuel gas side has a merge configuration. In this passageconfiguration, the oxidizing gas passage R1 extends in series in theorder of the cell CC, CB and CA and the coolant passage R3 meanderinglyextends in the same direction as that of the oxidizing gas passage R1;and a fuel gas passage R2A is provided in the cell CA in such a manneras to extend in the direction opposite to the oxidizing gas passage R1,a fuel gas passage R2B is provided in the cell CB in such a manner as toextend in parallel to the fuel gas passage R2A, and a fuel gas passageR2 into which the fuel gas passages R2A and R2B merge is provided in thecell CC in such a manner as to flow in the same direction as that of theoxidizing gas passage R1.

[0153] In this way, the fuel gas passages R2A and R2B are provided inparallel to each other, which passages R2A and R2B merge into the fuelgas passage R2. As a result, it is possible to effectively improve thehydrogen utilization ratio. It is to be noted that the same effects canbe obtained by allowing the oxidizing gas side to have a mergeconfiguration.

[0154]FIG. 33 shows a passage configuration of a four-cell structure inwhich the fuel gas side has a merge configuration. In this passageconfiguration, the oxidizing gas passage R1 extends in series in theorder of the cells CD, CC, CB and CA and the coolant passage R3 extendsin series in the same direction as that of the oxidizing gas passage R1;and a fuel gas passage R2A is provided in the cell CA, a fuel gaspassage R2B is provided in the cell CB, a fuel gas passage R2C isprovided in the cell CC, and a fuel gas passage R2 into which the fuelgas passages R2A, R2B and R2C merge is provided in the cell CD in such amanner as to extend in the same direction as that of the oxidizing gaspassage R1.

[0155] With this configuration, the same effects as those obtained bythe three-cell structure shown in FIG. 32 can be obtained. Inparticular, since a reduction in flow rate of the fuel gas due toconsumption is large, the adoption of the merge configuration of thefuel gas side is effective to easily improve the flow velocity of thefuel gas and also easily enhance the hydrogen utilization ratio.

[0156]FIG. 34 is an exploded perspective view of a solid polymerelectrolyte fuel cell assembly 200 according to a sixth embodiment ofthe present invention and FIG. 35 is a view showing flows of anoxidizing gas, a fuel gas, and a coolant in the cell assembly 200. Inthe cell assembly 200 according to this embodiment, parts correspondingto those in the cell assembly 10 according to the first embodiment aredesignated by the same reference numerals and the overlapped descriptionthereof is omitted.

[0157] The cell assembly 200 includes a first unit cell 202 and a secondunit cell 204 which are stacked to each other in the direction shown byan arrow A. The first unit cell 202 has a first unified body 206 and thesecond unit cell 204 has a second unified body 208. The first unifiedbody 206 is held between a first separator 210 and a first intermediateseparator 212, and the second unified body 208 is held between a secondintermediate separator 214 and a second separator 216. A third separator218 is stacked to the second separator 216.

[0158] The cell assembly 200 has, on a one-edge portion in the long-sidedirection, oxidizing gas inlets 36 a, coolant intermediate communicationholes 220, and oxidizing gas outlets 36 b which respectively passthrough the cell assembly 200 in the direction shown by an arrow A, andalso has, on the other edge portion in the long-side direction, coolantinlets 44 a, oxidizing gas intermediate communication holes 40, andcoolant outlets 44 b which respectively pass through the cell assembly200 in the direction shown by the arrow A. The cell assembly 200 has, ona one-edge portion in the short-side direction, fuel gas inlets 42 a andfuel gas outlets 42 b which respectively pass through the cell assembly200, and also has, on the other edge portion in the short-sidedirection, fuel gas intermediate communication holes 38 which passthrough the cell assembly 200 in the direction shown by the arrow A.

[0159] The second intermediate separator 214 has a plurality of linearcoolant passages 222 communicated to both the coolant inlet 44 a and thecoolant intermediate communication hole 220 of the second intermediateseparator 214. The third separator 218 has a plurality of linear coolantpassages 224 communicated to both the coolant intermediate communicationhole 220 and the coolant outlet 44 b of the third separator 218.

[0160] In the cell assembly 200 configured as described above, in eachof the first and second unified bodies 206 and 208, the oxidizing gasand fuel gas are supplied in series in the directions perpendicular toeach other, with a result that the same effects as those obtained by thefirst embodiment, such as equalization of humidities and improvement ofthe drainage characteristic can be obtained.

[0161]FIG. 36 is an exploded perspective view of a solid polymerelectrolyte fuel cell assembly 240 according to a seventh embodiment ofthe present invention, and FIG. 37 is a view showing flows of anoxidizing gas, a fuel gas, and a coolant in the cell assembly 240. Inthe cell assembly 240 according to this embodiment, parts correspondingto those in the cell assembly 200 according to the sixth embodimentshown in FIG. 34 are designated by the same reference numerals and theoverlapped description thereof is omitted.

[0162] The cell assembly 240 includes a first unit cell 242 and a secondunit cell 244 which are stacked in the direction shown by an arrow A.The cell assembly 240 has, on a one-edge portion in the long-sidedirection, oxidizing gas inlets 36 a, coolant outlets 44 b, coolantinlets 44 a, and fuel gas intermediate communication holes 38 whichrespectively pass through the cell assembly 240 in the direction shownby the arrow A, and also has, on the other edge portion in the long-sidedirection, fuel gas inlets 42 a, coolant intermediate communicationholes 220, and oxidizing gas intermediate communication holes 40 whichrespectively pass through the cell assembly 240 in the direction shownby the arrow A. The cell assembly 240 has, on a one-edge portion in theshort-side direction, oxidizing gas outlets 36 b and fuel gas outlets 42b which respectively pass through the cell assembly 240 in the directionshown by the arrow A.

[0163] A first intermediate separator 212 has oxidizing gas passages 246meandering along a surface facing to a cathode 24 a of a first unifiedbody 206, and a second separator 216 has oxidizing gas passages 248meandering along a surface facing to a cathode 24 b of a second unifiedbody 208. The oxidizing gas passages 246 are communicated to both theoxidizing gas inlet 36 a and the oxidizing gas intermediatecommunication hole 40 of the first intermediate separator 212. Theoxidizing gas passages 248 are communicated to both the oxidizing gasintermediate communication hole 40 and the oxidizing gas outlet 36 b ofthe second separator 216.

[0164] As shown in FIG. 37, a first separator 210 has fuel gas passages250 meandering along a surface facing to an anode 26 a of the firstunified body 206, and a second intermediate separator 214 has fuel gaspassages 252 meandering along a surface facing to an anode 26 b of thesecond unified body 208. The fuel gas passages 250 are communicated toboth the fuel gas inlet 42 a and the fuel gas intermediate communicationhole 38 of the first separator 210, and the fuel gas passages 252 arecommunicated to both the fuel gas intermediate communication hole 38 andthe fuel gas outlet 42 b of the second intermediate separator 214.

[0165] In the cell assembly 246 configured as described above, theoxidizing gas supplied to the cell assembly 240 flows along themeandering, oxidizing gas passages 246 and 248 communicated in series toeach other, and the fuel gas supplied to the cell assembly 240 flows inthe meandering gas passages 250 and 252 communicated in series to eachother. Accordingly, the length of the gas passages for each of theoxidizing gas and fuel gas is made relatively greater, with a resultthat the same effects as those obtained by the first embodiment, such asequalization of humidities and improvement in drainage characteristiccan be obtained. Although certain preferred embodiments of the presentinvention have been shown and, described in detail, it should beunderstood that various changes and modifications may be made thereinwithout departing from the scope of the appended claims.

[0166] Industrial Applicability

[0167] In the solid polymer electrolyte fuel cell assembly and the fuelcell stack according to the present invention, the cell assembly isconfigured by stacking a plurality of unit cells to each other and thereaction gas passages are provided such that at least portions thereofare communicated in series to each other over respective unit cells, andaccordingly, it is possible to easily equalize humidities and easilyimprove the drainage characteristic, and further, since the fuel cellstack is assembled by stacking the cell assembles to each other, it ispossible to effectively improve the workability of the assembly of thefuel cell stack.

[0168] In the method of supplying a reaction gas to a fuel cellaccording to the present invention, the reaction gas is supplied inseries to a plurality of unit cells constituting each cell assembly, andaccordingly, it is possible to increase the flow rate, flow velocity,and pressure drop of the reaction gas, and hence to effectively improvethe reaction performance of each unit cell.

1. A solid polymer electrolyte fuel cell assembly (10) comprising aplurality of unit cells (14, 16) stacked to each other, said unit cells(14, 16) each having a unified body (18, 20) including an anode (26 a,26 b), a cathode (24 a, 24 b), and a solid polymer electrolyte membrane(22 a, 22 b) disposed between said anode (26 a, 26 b) and said cathode(24 a, 24 b), wherein reaction gas passages (52, 56, 46, 58) forallowing at least one of reaction gases of a fuel gas and an oxidizinggas to flow in said unit cells (14, 16) are provided in said cellassembly (10) in such a manner that at least portions of said reactiongas passages (52, 56, 46, 58) are communicated in series to each otherover said unit cells (14, 16).
 2. A solid polymer electrolyte fuel cellassembly (10) according to claim 1, wherein at least two of said unitcells (14, 16) in said cell assembly (10) have structures different fromeach other.
 3. A solid polymer electrolyte fuel cell assembly (10)according to claim 2, wherein said reaction gas passages (52, 56, 46,58) provided in at least two of said unit cells (14, 16) havecross-sections different from each other.
 4. A solid polymer electrolytefuel cell assembly (10) according to claim 3, wherein the cross-sectionsof said reaction gas passages (52, 56, 46, 58) provided in said at leasttwo unit cells (14, 16) are different from each other by making thedepths, widths, or the number of reaction gas passages provided in oneof said at least two unit cells (14, 16) different from the depths,widths, or the number of reaction gas passages provided in another ofsaid at least two unit cells (14, 16).
 5. A solid polymer electrolytefuel cell assembly (10) according to claim 3 or 4, wherein saidcross-sections of said reaction gas passages (52, 58) on a downstreamside in a flow direction of the reaction gas is smaller than saidcross-sections of said reaction gas passages (56, 46) on an upstreamside in the flow direction of the reaction gas.
 6. A solid polymerelectrolyte fuel cell assembly (10) according to claim 2, wherein alength of said reaction gas passages (52, 58) on a downstream side in aflow direction of the reaction gas is greater than a length of saidreaction gas passages (56, 46) on an upstream side in the flow directionof the reaction gas.
 7. A solid polymer electrolyte fuel cell assembly(10) according to claim 2 or 6, wherein said reaction gas passages (52,56, 46, 58) provided in said at least two unit cells (14, 16) haveshapes different from each other.
 8. A solid polymer electrolyte fuelcell assembly (10) according to claim 2, wherein said unified bodies(82, 84) provided in said at least two unit cells (14, 16) are differentfrom each other.
 9. A solid polymer electrolyte fuel cell assembly (10)according to claim 8, wherein a heat resistance of said unified body(84) on an downstream side in a flow direction of the reaction gas ishigher than a heat resistance of said unified body (82) on a upstreamside in the flow direction of the reaction gas.
 10. A solid polymerelectrolyte fuel cell assembly (10) according to claim 9, wherein saidunified body (82) on the upstream side in the flow direction of thereaction gas is provided with a fluorine based membrane; and saidunified body (84) on the downstream side in the flow direction of thereaction gas is provided with a hydrocarbon based membrane.
 11. A solidpolymer electrolyte fuel cell assembly (10) according to claim 1,wherein a separator (28) is interposed between adjacent two of saidunified bodies (18, 20); and said separator (28) has a reaction gassupply communication hole (36 a) for supplying the reaction gas intosaid reaction gas passages (46) provided in each of said unit cells (14,16) and a reaction gas discharge communication hole (36 b) fordischarging the reaction gas from said reaction gas passages (46)provided in each of said unit cells (14, 16).
 12. A Solid polymerelectrolyte fuel cell assembly (10) according to claim 1, wherein aseparator (28) is interposed between adjacent two of said unified bodies(18, 20), and said separator (28) is configured as a metal plate havingprojections and depressions corresponding to shapes of said reaction gaspassages.
 13. A solid polymer electrolyte fuel cell assembly (10)according to claim 12, wherein said separator (32) has fuel gas passages(56) as said reaction gas passages on a side facing to one (18) of saidunified bodies, and also has oxidizing gas passages (58) as saidreaction gas passages on a side facing to the other (20) of said unifiedbodies.
 14. A solid polymer electrolyte fuel cell assembly (10)according to claim 1, wherein said reaction gas passages (52, 56, 46,58) are set such that the reaction gas passes along a reaction plane ofone (14) of the adjacent two of said unit cells, flows in the stackingdirection of said unit cells, and flows on a reaction plane of the other(16) of the adjacent two of said unit cells.
 15. A solid polymerelectrolyte fuel cell assembly (10) according to claim 14, wherein saidreaction gas passages (52, 56, 46, 58) meanderingly extend in thestacking direction of said unit cells (14, 16).
 16. A solid polymerelectrolyte fuel cell assembly (10) according to claim 1 or 14, whereina flow direction of said fuel gas in fuel gas passages (52, 56) of saidreaction gas passages along the reaction plane of said unit cell (14,16) is opposite to a flow direction of said oxidizing gas in oxidizinggas passages (46, 58) of said reaction gas passages along the reactionplane of said unit cell (14, 16).
 17. A solid polymer electrolyte fuelcell assembly (10) according to claim 1 or 14, wherein fuel gas passages(52, 56) of said reaction gas passages are provided in series in saidplurality of unit cells (162, 164); and oxidizing gas passages (46, 58)of said reaction gas passages are provided in parallel in said pluralityof unit cells (162, 164).
 18. A solid polymer electrolyte fuel cellassembly (10) according to claim 1 or 14, wherein fuel gas passages (52,56) and oxidizing gas passages (46, 58) of said reaction gas passagesare provided in such a manner as to linearly extend along the reactionplane of said unit cell (14, 16).
 19. A solid polymer electrolyte fuelcell assembly (10) according to claim 14 or 18, wherein said fuel gaspassages (52, 56) or said oxidizing gas passages (46, 58) of saidreaction gas passages are provided with a reaction gas inlet (42 a, 36a) and a reaction gas outlet (42 b, 36 b) on one side of a plane of saidunit cell (14, 16).
 20. A solid polymer electrolyte fuel cell assembly(10) according to claim 14 or 15, wherein an intermediate communicationhole (38, 40) communicated to said reaction gas passages is provided foreach of said unit cells (14, 16) in such a manner as to extend in thestacking direction of said unit cells (14, 16); and said reaction gaspassages form an approximately U-shaped flow line extending from onereaction gas inlet (42 a, 36 a) of one (14) of said unit cells to areaction gas outlet, (42 b, 36 b) of the other (16) of said unit cellsthrough said intermediate communication hole (38, 40).
 21. A solidpolymer electrolyte fuel cell assembly (10) according to claim 1,wherein coolant passages (48) are provided with said plurality of saidunit cells (14, 16) put therebetween while being located on both sidesof said unit cells (14, 16) in the stacking direction of said unit cells(14, 16).
 22. A solid polymer electrolyte fuel cell assembly (10)according to claim 21, wherein said coolant passages (48) are closer toan oxidizing gas passage (46) provided in said unit cell (14) on theupstream side in the flow direction of the oxidizing gas as comparedwith an oxidizing gas passage (58) provided in said unit cell (16) onthe downstream side in the flow direction of the oxidizing gas.
 23. Asolid polymer electrolyte fuel cell-assembly (10) according to claim 21or 22, wherein coolant inlets (44 a) and coolant outlets (44 b)communicated to said coolant passages (48) are provided on one side ofsaid unit cells (14, 16).
 24. A solid polymer electrolyte fuel cellassembly (10) according to any one of claims 21 to 23, wherein saidcoolant passages (48) form an approximately U-shaped flow line forallowing the coolant to flow from said coolant inlet (44 a) to one sideof a partition wall member (34), flow along the one side of saidpartition wall member (34), flow to the other side of said partitionwall member (34) via an intermediate return portion (50), and flow inthe opposite direction along the other side of said partition wallmember (34).
 25. A solid polymer electrolyte fuel cell assembly (10)according to claim 24, wherein said coolant passage (48) is provided insuch a manner as to linearly extend along a plane of said unit cell (14,16).
 26. A solid polymer electrolyte fuel cell assembly (10) comprisinga plurality of unit cells (14, 16) stacked to each other, said unitcells (14, 16) each having a unified body (18, 20) including an anode(26 a, 26 b), a cathode (24 a, 24 b), and a solid polymer electrolytemembrane (22 a, 22 b) between said anode (26 a, 26 b) and said cathode(24 a, 24 b), wherein coolant passages (48, 54) communicated to eachother in series are formed on both sides of said unit cells (14, 16) inthe stacking direction of said unit cells (14, 16).
 27. A fuel cellstack comprising a stack of a plurality of cell assemblies (10), whereineach of said cell assemblies (10) comprises a plurality of unit cells(14, 16) stacked to each other, said unit cells (14, 1,6) each having aunified body (18, 20) including an anode (26 a, 26 b), a cathode (24 a,24 b), and a solid polymer electrolyte membrane (22 a, 22 b) betweensaid anode (26 a, 26 b) and said cathode (24 a, 24 b); and reaction gaspassages (52, 56, 46, 58) for allowing at least one of reaction gases ofa fuel gas and an oxidizing gas to flow in said unit cells (14, 16) areprovided in said cell assembly (10) in such a manner that at leastportions of said reaction gas passages (52, 56, 46, 58) are communicatedin series to each other over said unit cells (14, 16).
 28. A fuel cellstack according to claim 27, wherein at least two of said unit cells(14, 16) in said cell assembly (10) have structures different from eachother.
 29. A fuel cell stack according to claim 27 or 28, wherein acoolant passage (48, 54) is provided only between adjacent two of saidcell assemblies (10).
 30. A fuel cell stack according to claim 27 or 28,wherein a reaction gas supply communication hole (36 a, 42 a) and areaction gas discharge communication hole (36 b, 42 b), which are openedin the stacking direction of said fuel cell stack (12), are provided;and intermediate communication holes (40, 38) opened in the stackingdirection of said fuel cell stack (12) are provided in a flow linebetween, said reaction gas supply communication hole (36 a, 42 a) andsaid reaction gas discharge communication hole (36 b, 42 b).
 31. A fuelcell stack according to claim 30, wherein each of said intermediatecommunication holes (40, 38) is provided in a flow line between areaction gas inlet (36 a, 42 a) provided in a plane of one (14) ofadjacent two of said unit cells and a reaction gas outlet (36 b, 42 b)provided in a plane of the other (16) of the adjacent two of said unitcells.
 32. A fuel cell stack according to claim 30, wherein saidintermediate communication hole (40, 38) is provided for communicatingadjacent two of said unit cells (14, 16) provided in adjacent two ofsaid cell assemblies (10) to each other.
 33. A fuel cell stack accordingto claim 30, wherein said intermediate communication hole (40, 38) isprovided for communicating adjacent two of said unit cells (14, 16) onlyin one of said cell assemblies (10) to each other.
 34. A fuel cell stackcomprising a stack of a plurality of cell assemblies (10), wherein eachof said plurality of cell assemblies (10) comprises a plurality of unitcells (14, 16) stacked to each other, said unit cells (14, 16) eachhaving a unified body (18, 20) including an anode (26 a, 26 b), acathode (24 a, 24 b), and a solid polymer electrolyte membrane (22 a, 22b) between said anode (26 a, 26 b) and said cathode (24 a, 24 b); andcoolant passages (48, 54) communicated to each other in series areformed on both sides of said unit cells (14, 16) in the stackingdirection of said unit cells (14, 16).
 35. A method of supplying areaction gas to a solid polymer electrolyte fuel cell assembly (10)comprising a plurality of unit cells (14, 16) stacked to each other,said unit cells (14, 16) each having a unified body (18, 20) includingan anode (26 a, 26 b), a cathode (24 a, 24 b), and a solid polymerelectrolyte membrane (22 a, 22 b) between said anode (26 a, 26 b),; andsaid cathode (24 a, 24 b), wherein reaction gas passages (52, 56, 46,58) for allowing at least one of reaction gases of a fuel gas and anoxidizing gas to flow in said unit cells (14, 16) are provided in saidcell assembly (10) in such a manner that at least portions of saidreaction gas passages(52, 56, 46, 58) are communicated in series to eachother over said unit cells (14, 16), said method comprising the stepsof: supplying the reaction gas from a reaction gas supply communicationhole (42 a, 36 a) to a plurality of reaction gas passages (52, 56, 46,58) in said unit cells (14, 16) in parallel, to subject the reaction gasflowing in said reaction gas passages (52, 56, 46, 58) to cell reaction;and discharging the spent reaction gas to reaction gas dischargecommunication holes (42 b, 36 b).
 36. A method of supplying a reactiongas according to claim 35, wherein the reaction gas is introduced insaid unit cell (14) on the upstream side in the flow direction of thereaction gas to be used for cell reaction, and is then introduced, viaan intermediate communication hole (40, 38), in said unit cell (16) onthe downstream side in the flow direction of the reaction gas to be usedfor cell reaction.
 37. A method of supplying a reaction gas according toclaim 35 or 36, wherein the reaction gas in an amount required forreaction in the whole of said cell assembly (10) is introduced in saidunit cell (14) on the most upstream side in the flow direction of thereaction gas.
 38. A method of supplying a reaction gas according toclaim 36, wherein the reaction gas is an oxidizing gas; and a coolant issupplied in coolant passages (48) which are closer to an oxidizing gaspassage (46) provided in said unit cell (14) on the upstream side in theflow direction of the oxidizing gas as compared with an oxidizing gaspassage (58) provided in said unit cell (16) on the downstream side inthe flow direction of the oxidizing gas.